Manhole covers are used to close manholes leading from street level down to a sewer or other utility connections. Of course, before such manholes can be entered their covers must be removed. Such covers are usually made of cast iron and tend to be difficult to handle because of their size and weight. For example, some manhole covers can weigh up to 200-300 pounds. Pick axes have typically been used to lift manhole covers. In doing so, the point of the pick ax is first inserted into a peripheral notch or a hole in the center of the manhole cover, so that it can be tilted upwardly and then carried or rolled away to expose the manhole. These manual steps must then be reversed to replace the cover. Injuries to the back, hands and fingers of the workmen have not been uncommon due to the difficulties in handling heavy manhole covers.
Specialized devices have recently been developed to facilitate moving manhole covers. For example, U.S. Pat. No. 4,365,925 shows a manhole cover lifter with a lever arm including a handle at its long end and a hook at its short end, fulcrumed about a pair of wheels so that the cover can be lifted and then rolled into or out of position. U.S. Pat. No. 4,157,811 shows a device wherein the lever arm pivots about vertical as well as horizontal axes on a base positioned next to the manhole so that the cover can be rotated into and out of position while lifted. These devices are essentially levers that provide some mechanical advantage, but still require a fair amount of manual effort.
Powered devices for this purpose have also been available. For example, U.S. Pat. No. 4,181,290 shows another manhole cover lifter with an arm that pivots about a horizontal axis in a base stabilized by retractable legs, but the arm is actuated by a fluid cylinder or a hand operated cable reel on a vertical column extending upwardly from the base. The cover is secured to the arm by adjustable edge pins and a center hook. However, this device only functions to raise the cover to a vertical position adjacent to the manhole and is not adapted to facilitate positioning the cover away from the manhole. After the cover is lifted it is desireable to move it away from the hole for convenient access by workmen and/or their equipment. Aside from interfering with access to the hole, there is also the question of safety should the cover slip or the device tip over.
A need has thus arisen for an improved manhole cover lifter which is not only adapted to engage any type of metallic cover, regardless of the notches or holes therein, but which is designed to hold the cover in a minimum raised position within surrounding framework which can be rolled away from the hole and secured for maximum access and safety.